#include<iostream>
#include<string.h>
#include<bits/stdc++.h>
using namespace std;

class Solution {
public:
    bool isPalindrome(string s) {
        int left = 0, right = s.size() - 1;
        while (left < right)
        {
            while (left < right && !isalnum(s[left])) ++left;

            while (left < right && !isalnum(s[right])) --right;

            if (left < right)
            {
                if (tolower(s[left]) != tolower(s[right]))
                {
                    return false;
                }
                ++left;
                --right;
            }
        }
        return true;
    }
};